A hydrogen generation assembly, or hydrogen-producing fuel processing assembly, is an assembly that converts one or more feedstocks into a hydrogen-containing gas stream containing hydrogen gas as a majority component. The produced hydrogen gas may be used in a variety of applications. One such application is energy production, such as in electrochemical fuel cells. An electrochemical fuel cell is a device that converts a fuel and an oxidant to electricity, a reaction product, and heat. For example, fuel cells may convert hydrogen and oxygen into water and electricity. In such fuel cells, the hydrogen gas is the fuel, the oxygen gas is the oxidant, and the water is a reaction product. Fuel cells are typically coupled together to form a fuel cell stack.
A hydrogen-producing fuel cell system is a hydrogen-producing fuel processing assembly that also includes a fuel cell stack that is adapted to receive hydrogen gas produced by the fuel processing assembly and to generate an electric current therefrom. The hydrogen-producing fuel processing assembly includes a hydrogen-producing region in which hydrogen gas is produced as a majority reaction product from one or more feedstocks. The reaction conditions in the hydrogen-producing region may affect the performance of the hydrogen generation assembly. This, in turn, may affect the performance of the fuel cell stack, the hydrogen-producing fuel cell system, and/or its ability to satisfy an applied load thereto. Accordingly, hydrogen-producing fuel processing assemblies and hydrogen-producing fuel cell systems will typically include various controls for regulating the reaction conditions in the hydrogen-producing region. Typically, these controls include a variety of manual and/or computerized controls.
To efficiently produce hydrogen gas, the hydrogen-producing region of the fuel processing assembly should be maintained at the desired operating conditions, including temperatures and pressures in a predetermined range for producing hydrogen gas. The product hydrogen stream from the hydrogen-producing region may be purified, if needed, and thereafter used as a fuel stream for a fuel cell stack, which produces an electric current from the product hydrogen stream and an oxidant, such as air. This electric current, or power output, from the fuel cell stack may be utilized to satisfy the energy demands of an energy-consuming device.
A consideration with any hydrogen-producing fuel processing assembly and/or fuel cell system is the ability to maintain the hydrogen generation region within a range of efficient reaction conditions. Maintaining the temperature of the hydrogen-producing region is a challenge in the design and operation of a hydrogen generation assembly. The particular optimal temperature range for a hydrogen-producing region may vary based upon such factors as the type of hydrogen-producing mechanism to be utilized, the particular feedstock(s) being used, etc. In many applications, optimal reaction conditions are maintained by manual control, while in other situations the reaction conditions may be maintained at peak efficiency by a microprocessor-based controller assembly. When the hydrogen generation assembly is already at a suitable hydrogen-producing temperature, the fuel cell system may be able to operate with a minimum of outside influence as long as the demand for hydrogen gas remains relatively constant. However, as this demand and/or other reaction conditions, or operating parameters, of the hydrogen-producing region change, the efficiency and/or stability of the hydrogen generation assembly (and/or fuel cell system) may quickly diminish. When the hydrogen generation assembly is not already at or near a desired hydrogen-producing temperature, the assembly may require some external influence or control to be applied.
Conventionally, microprocessor-based controllers have been used to provide control signals that can maintain the hydrogen-producing region of a hydrogen generation assembly within a suitable hydrogen-producing temperature range in the absence of direct human intervention. One approach is to include a series of valves or other system-altering inputs that may be used to manipulate the flow of reactants and/or energy inputs to the hydrogen-producing region. However, the ability of such a controller is limited, and may depend on its programming, its being free from operational interruption, the input signals with which it is provided, and so on.